I suspect that Black Swan author, Nassim Nicholas Taleb would agree with the possibility described in this article!
In the United States, Hachette doesn’t have quite the same market share. But it performs better than any of the other houses because of the strengths of the Patterson and Meyer publishing franchises. As secular changes batter the industry overall, Hachette may benefit from its more efficient publishing operations—few titles that generate more sales and greater profits—to become the only vibrant, healthy publishing house.
via Will Hachette Be the Last Publisher Standing? | The Big Money.
Eoin Purcell's Blog 
How awful if the book publishing world was reduced to Patterson and Meyer, what a nightmare prospect. I for one would long since have given up by then.
I suspect strongly that while the “top tier” publishers will probably looks something like a collection of uber brands, publishing will be much more vibrant that that suggests.
Eoin